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Summary Objective Based on simultaneous voice and electroglottograph (EGG) signals, to gain a better understanding of human voice production process, to make pitch-synchronous segmentation of voice signals, and to make visual representations of pitch marks and timbre spectra with high resolution. Methods/Design The traditional spectrogram segments the voice signals with a process window of fixed size and fixed shift, then performs fast Fourier transformation after multiplied with a window function, typically a Hamming window. Then display power spectrum in both frequency and time. Pitch information and timbre information are mixed. The new design segments the signals into pitch periods, either using the derivatives of the EGG signals or based on the voice signals, then performs Fourier analysis to the segment of signals in each pitch period without using a window function. The pitch information and the timbre information are cleanly separated. The graphical representations of both pitch marks and timbre spectra exhibit high resolution and high accuracy. Results Detailed analysis of simultaneously acquired voice and EGG signals provides a more precise understanding of human-voice production process. The transient theory of voice production, proposed by Leonhard Euler in early 18th century, is substantiated with modern data. Based on the transient theory of voice production, a pitch-synchronous spectrogram software is developed, which makes a visual representation of pitch marks and timbre spectra. In addition, the timbre spectrum and the power evolution pattern in each pitch period can be displayed individually. Conclusions Simultaneously acquired voice and EGG signals indicates that each glottal closing triggers a decaying elementary wave in the vocal tract. A superposition of those elementary waves constitutes voice. Based on that concept and using EGG data, a pitch-synchronous voice signal processing method is developed. The voice signal is first segmented into pitch periods, then the two ends are equalized. Fourier analysis is applied to obtain the timbre spectrum of each pitch period. High resolution display of timbre spectrum is generated. The power evolution pattern in each pitch period is also displayed.

The concept of wavefunction was introduced in the first 1926 paper by Erwin Schrödinger as the central object of the atomic world and the cornerstone of quantum mechanics. It is a mathematical representation of de Broglie’s postulate that the electron is a material wave. It was defined as everywhere real, single-valued, finite, and continuously differentiable up to the second order. Nevertheless, for many decades, wavefunction has not been characterized as an observable. First, it is too small. The typical size is a small fraction of a nanometer. Second, it is too fragile. The typical bonding energy of a wavefunction is a few electron volts. The advancement of STM and AFM has made wavefunctions observable. The accuracy of position measurement is in picometers. Both STM and AFM measurements are non-destructive, which leaves the wavefunctions under observation undisturbed. Finally, the meaning of direct experimental7 observation and mapping of wavefunctions is discussed.

This chapter discusses the physics and properties of four types of atomic forces occurring in STM and AFM: the van der Waals force, the hard core repulsion, the ionic bond, and the covalent bond. The general mathematical form of the van der Waals force between a tip and a flat sample is derived. The focus of this chapter is the covalent-bond force, which is a key in the understanding of STM and AFM. The concept of covalent bond is illustrated by the hydrogen molecular ion, the prototypical molecule used by Pauling to illustrate Heisenberg's concept of resonance. The Herring-Landau perturbation theory of the covalent bond, an analytical incarnation of the concept of resonance, is presented in great detail. It is then applied to molecules built from many-electron atoms, to show that the perturbation theory can be applied to practical systems to produce simple analytic results for measurable physical quantities with decent accuracy.

This chapter discusses various methods for tip treatment. First, a general discussion about the experimental facts of STM and AFM tips is presented, which points to the subtleties and significance of the last few atoms at the tip apex. The standard method of making an STM tip is the electrochemical etching of a tungsten wire. The experimental procedure is described in detail. The study of the tip using field-ion microscopy is outlined. The tungsten tips freshly made from electrochemical etching often do not provide atomic resolution. Ex-situ and in-situ tip treatments are necessary. Several ex-situ tip treatment methods are described, inducing annealing, field evaporation, and annealing with a field. In-situ tip treatment method such as high-field treatment and controlled collision are described. Then, tip treatment for electrochemical STM is described. Tip treatment methods for spin-polarized STM are described. Finally, tip functionalization, especially with Xe atom and CO molecule, is described.

This chapter discusses electronics and computer interfaces for STM and AFM. For STM, the detection of the minute tunneling current is of paramount importance. Thus, the basic concepts and analysis of the current amplifier, or more accurately speaking, the transimpedence amplifier, is discussed. It includes the typical circuits and an analysis of the gain, noise, frequency response, microphone effect due to the coaxial cable, and the logarithmic amplifier to make the distance dependence of the output signal linear. the feedback system is then discussed, including a typical circuit, as well as the analyses of the steady-state response and the transient response. Finally, the architecture of the computer interface system with the algorithm of automatic approaching is discussed.

This chapter presents the basic designs and working principles of STM and AFM, as well as an elementary theory of tunneling and the imaging mechanism of atomic resolution. Three elementary theories of tunneling are presented: the one-dimensional Schrödinger’s equation in vacuum, the semi-classical approximation, and the Landauer formalism. The relation between the decay constant and the work function, and a general expression of tunneling conductance versus tip-sample distance are derived. A brief summary of experimental facts on the mechanism of atomic resolution STM and AFM is presented, which leads to a picture of interplay between the atomic states of the tip and the sample, as well as the role of partial covalent bonds formed between those electronic states. Four illustrative applications are presented, including imaging self-assembed molecules on solid-liquid interfaces, electrochemical STM, catalysis research, and atom manipulation.

This chapter discusses the imaging mechanism of STM and AFM at the atomic scale. Experimental facts show that at atomic resolution, tip electronic states play a key role. Analytic theoretical treatments provide quantitative explanation of the effect of the tip electronic states. On transition-metal tips, first-principle studies unanimously show that d-type tip electronic states dominate the Fermi-level DOS. First-principle studies of the combined tip-sample systems show that for both STM and AFM, the p- and d-type tip electronic states are the keys to understanding the atomic-scale images. The case of spin-polarized STM and the chemical identification of surface atoms are also discussed in terms of tip electronic structure. The chapter concludes with discussions of experimental verifications of the reciprocity principle: at atomic resolution, the role of tip electronic states and the sample electronic states are interchangeable.

This chapter discusses vibration isolation of STM and AFM. First, the basic concepts of vibration isolation are illustrated by a one-dimensional system using elementary mechanics. The source of vibration, the environmental vibration, its characteristics, and methods of measurement are presented. The importance of vibration isolation at the laboratory foundation level and the proper mechanical design of STM and AFM are then discussed. The focus of this chapter in on the most important vibration isolation system: two-stage suspension spring with eddy-current damping. A detailed analysis of the two-stage spring system as well as aspects of practical design is presented. The principles and design charts for eddy-current damping system are discussed. Finally, the commercial pneumatic vibration isolation system is briefly discussed.

This chapter presents systematic methods to evaluate the tunneling matrix elements in the Bardeen tunneling theory. A key problem in applying the Bardeen tunneling theory to STM is the evaluation of the tunneling matrix elements, which is a surface integral of the wavefunctions of the tip and the sample, roughly in the middle of the tunneling gap. By expanding the tip wavefunction in terms of spherical harmonics and spherical modified Bessel functions, very simple analytic expressions for the tunneling matrix elements are derived: the tunneling matrix elements are proportional to the amplitudes or the corresponding x-, y-, or z-derivatives of the sample wavefunction at the center of the tip. Two proofs are presented. The first proof is based on the Green’s function of the Schrödinger’s equation in vacuum. The second proof is based on a power-series expansion of the tip wavefunctions.

In this tribute article to D.G. Miller, we review some historical and recent contributions to understanding the myoelastic-aerodynamic (MEAD) theory of phonation and the related acoustic phenomena in subglottal and vocal tract. At the time of the formulation of MEAD by van den Berg in late 1950s, it was assumed that vocal fold oscillations are self-sustained thanks to increased subglottal pressure pushing the glottis to open and decreased subglottal pressure allowing the glottis to close. In vivo measurements of subglottal pressures during phonation invalidated these assumptions, however, and showed that at low fundamental frequencies subglottal pressure rather tends to reach a maximum value at the beginning of glottal closure and then exhibits damped oscillations. These events can be interpreted as transient acoustic resonance phenomena in the subglottal tract that are triggered by glottal closure. They are analogous to the transient acoustic phenomena seen in the vocal tract. Rather than subglottal pressure oscillations, a more efficient mechanism of transfer of aerodynamic energy to the vocal fold vibrations has been identified in the vertical phase differences (mucosal waves) making the glottal shape more convergent during glottis opening than during glottis closing. Along with other discoveries, these findings form the basis of our current understanding of MEAD.

The imaging mechanism of scanning tunnelling microscopy (STM) and non-contact atomic force microscopy (NC-AFM) has the same origin, that is, the interaction between the electronic states of the tip and the electronic states of the sample. Therefore, using a well-characterized sample, the tip electronic states become the object to be probed by both STM and AFM. In this paper, we will present an analytic approach to compute the force distribution and the tunnelling-conductance distribution. As an example, we predict the possibility of resolving the lateral profiles of the tetrahedral hybrid orbitals, which are the foundation of many important materials essential to industry and life. We will discuss the conditions under which it could be observed, together with the issue of reproducibility.

The imaging mechanism for both NC-AFM and STM at atomic resolution can be considered as a process of making and breaking of chemical bonds between the tip and the sample. Based on that concept, a universal relation between tunnelling conductance G and attractive atomic force F is established, which can be verified experimentally. This further implies an experimentally verifiable relation between the threshold resistance R and diffusion activation energy E in atom manipulation.

We present a novel quartz cantilever for frequency-modulation atomic force microscopy (FM-AFM) which has three electrodes: an actuating electrode, a sensing electrode, and a ground electrode. By applying an ac signal on the actuating electrode, the cantilever is set to vibrate. If the frequency of actuation voltage closely matches one of the characteristic frequencies of the cantilever, a sharp resonance should be observed. The vibration of the cantilever in turn generates a current on the sensing electrode. The arrangement of the electrodes is such that the cross-talk capacitance between the actuating electrode and the sensing electrode is less than 10(-16) F, thus the direct coupling is negligible. To verify the principle, a number of samples were made. Direct measurements with a Nanosurf easyPPL controller and detector showed that for each cantilever, one or more vibrational modes can be excited and detected. Using classical theory of elasticity, it is shown that such novel cantilevers with proper dimensions can provide optimized performance and sensitivity in FM-AFM with very simple electronics.

The problem of determining and understanding the role of tip electronic states is one of the central and critical scietific problems in scanning tunneling microscopy (STM) and spectroscopy (STS). In this paper, we described a theory and a practical method for in-situ characterization of the tip electronic states. The method consists of a deconvolution procedure, from which the density of states (DOS) of the tip is recovered from the measured tunneling spectra. The tip DOS, obtained from deconvolving an experimental tunneling spectrum, can be compared with predictions of first-principle numerical calculations of various realistic tip structures, or independent measurements, for example, field emission spectroscopy and photoemission spectroscopy. The reference tunneling spectrum of the sample can be obtained using a flat-DOS blunt tip, for example, following the tip-treatment process described by Feenstra et al. Using the deconvolution method, we analyzed the STM and STS data published by Pelz. The results indicates that the W tip picked up a Si cluster in the middle of a scan on a Si sample. To further clarify the role of tip electronic states in STM imaging process, a set of new experiments is proposed.

The tube scanner, a piezoelectric ceramic tube with the outer metal coating sectioned into four quadrants, is widely used in scanning probe microscopes. Based on stress-and-strain analysis, we obtain analytic expressions for the deflections of tube scanners, which are found to be in good agreement with the results of finite-element analyses and experimental measurements. Also, we show that by applying an AC voltage on one of the quadrants, an AC current of well-defined intensity and phase is generated from each of the other three quadrants to the ground (inner metal coating). This current can be used to measure the piezoelectric coefficient and to inspect the uniformity and geometrical accuracy of tube scanners. A combination of those who results provides an easy and accurate method for testing and calibrating tube scanners in situ, for example, in a vacuum chamber or in a cryostat.

A fundamental study of the self-induced repair (SIR) of constrictions is presented. SIR is a local electrodeposition process induced by the Joule heating at a constriction, together with the temperature dependence of the equilibrium potential at a metal-electrolyte interface

In scanning tunneling microscopy (STM), the potential barriers are often close to or lower than the Fermi level, where both semiclassical tunneling theory and Bardeen’s tunneling theory are no longer valid. We present a new perturbation approach for general quantum transmission phenomena. For thick, positive potential barriers, it reduces to Bardeen’s tunneling theory. For potential barriers lower than the energy level, it is valid as long as the barrier thickness is smaller than one half of the de Broglie wavelength, a condition which is always satisfied in STM. An immediate application is shown.

We present a theory of the atomic resolution in scanning tunneling microscopy (STM) in terms of localized surface states on the tip. The tunneling matrix elements arising from these tip states are evaluated with the derivative rule. For example, a pz surface state on the tip generates a tunneling matrix element proportional to [∂ψ/∂z] at the nucleus of the apex atom, and a d3z2−r 2 tip state generates a tunneling matrix element proportional to [3∂2ψ/∂z2−κ2ψ], (ψ is the sample wave function, κ is the decay constant of surface wave function, κ=(2meφ)1/2/ℏ ). To obtain analytic results of theoretical STM images, we further developed a simple independent‐orbital model to describe the wave functions of the sample surface. With this model, we present qualitative and quantitative explanations of the observed atomic resolution on metals and semiconductors, the spontaneous switching of instrument resolution during imaging, and various tip‐sharpening procedures.

This chapter presents a unified theory of tunneling phenomenon and covalent bond force, as a result of the similarity between the Bardeen theory of tunneling and the Herring-Landau theory of the covalent bond. Three general theoretical treatments are presented, which show that tunneling conductance is proportional to the square of the covalent bond interaction energy, or equivalently, the square of covalent bond force. The constant of proportionality is related to the electronic properties of the materials. For the case of a metal tip and a metal sample, an explicit equation contains only measurable physical quantities is derived. Several experimental verifications are presented. The equivalence of covalent bond energy and tunneling conductance provides a theoretical explanation of the threshold resistance observed in atom-manipulation experiments, and points to a method of predicting the threshold resistance for atom manipulation. Theory of imaging wavefunctions with AFM is discussed.

This chapter presents the basic designs and working principles of STM and AFM, as well as an elementary theory of tunneling and the imaging mechanism of atomic resolution. Three elementary theories of tunneling are presented: the one-dimensional Schrödinger's equation in vacuum, the semi-classical approximation, and the Landauer formalism. The relation between the decay constant and the work function, and a general expression of tunneling conductance versus tip-sample distance are derived. A brief summary of experimental facts on the mechanism of atomic resolution STM and AFM is presented, which leads to a picture of interplay between the atomic states of the tip and the sample, as well as the role of partial covalent bonds formed between those electronic states. As an introduction to the concept of equivalence of tunneling and atomic forces, atom and molecule manipulation is briefly presented.

This chapter discusses the imaging mechanism of STM at the nanometer scale, where the features of interest are of about one nanometer and up. Using an s-wave tip model, using the Bardeen tunneling theory, Tersoff and Hamann showed that the STM image in this case is tip-independent: it is determined by the local density of states of the bare sample surface at Fermi level, taken at the center of curvature of the tip. The Tersoff-Hamann model has found numerous applications in interpreting the STM images, from the superstructure of surface reconstruction to the confined or scattered waves of the surface states. However, as shown by Tersoff and Hamann in their original papers, for features much smaller than one nanometer, such as at the atomic features of 0.3 nm, the non-spherical electronic states of the tip could play a significant role and thus cannot be overlooked.

This chapter discusses the physical principle, design, and characterization of piezoelectric scanners, which is the heart of STM and AFM. The concept of piezoelectricity is introduced at the elementary level. Two major piezoelectric materials used in STM and AFM, quartz and lead zirconate titanate ceramics (PZT), are described. After a brief discussion of the tripod scanner and the bimorph, much emphasis is on the most important scanner in STM and AFM: the tube scanner. A step-by-step derivation of the deflection formula is presented. The in-situ testing and calibration method based on pure electrical measurements is described. The formulas of the resonance frequencies are also presented. To compensate the non-linear behavior of the tube scanner, an improved design, the S-scanner, is described. Finally, a step-by-step procedure to repole a depoled piezo is presented.

This chapter discusses various mechanical designs for STM and AFM. The central piece of the mechanical design of STM and AFM is the course positioner. Therefore, various types of course positioners are also discussed. The louse and the pocket-size STM are discussed first. It is of significant historical importance but no longer popular today. The single-tube STM has a very simple mechanical structure, and still the basis of the most popular commercial STM and AFM. The Besocke-type or the beetles is very popular among builders of special-purpose STM due its immunity to temperature variation and vibration. For STM requiring superb stability, the walker and the kangaroo are the preferred design. The commercial nanostepper, the Inchworm, is described. It has been successfully used by many designers of special-purpose STM.

This chapter presents basic experimental methods and the basic theory of tunneling. The classical metal-insulator-metal tunneling junction experiment of Giaever, designed to verify the Bardeen-Cooper-Schrieffer theory of superconductivity, is the motivation for Bardeen to invent his perturbation theory of tunneling. That Bardeen theory then became the starting point of the most useful models of STM. Section 2.2 presents the Bardeen tunneling theory from time-dependent perturbation theory of quantum mechanics, starting from a one-dimensional case, then proceeds to three-dimensional version with wave-function corrections. The Bardeen theory in second-quantization format, the transfer-Hamiltonian formalism, is also presented. As extensions of the original Bardeen theory, the theories and experiments of inelastic tunneling and spin-polarized tunneling are discussed in depth.